This invention relates to apparatus and a method for manufacturing optical lenses and, more particularly, to a carrier for precisely and accurately positioning an optical lens blank in machine tools such as a lathe or milling machine to enable formation of optical surfaces on the lens blank with minimal error or misalignment.
In the optical lens industry, and especially the intraocular lens industry, lenses adapted for substitution in the human eye after removal of a cataract, are currently manufactured using the following method. A disk-shaped lens blank, typically cut from a sheet of transparent optical material, is placed in a vacuum holding device and pressed onto an acrylic, cylindrical holding device commonly referred to as a dopt. A water soluble dental-type wax adheres the lens blank to the end surface of the cylindrical dopt. The dopt/lens blank assembly is then mounted in a lathe and the exposed side of the lens blank is machined or cut with a cutting tool to form the desired curvature for an optical surface. This method often produces significant inaccuracies, however, due to misalignment of the lens blank on the dopt and/or inaccuracies on the surfaces of the dopt on which the blank is secured. Such inaccuracies create improper angular relationships between the cut surface of the lens blank and other surfaces thereof such that the optical center of the lens being formed is misaligned requiring either rejection of the lens before use or resulting in inaccurate vision if used.
Many intraocular lenses also require formation of optical surfaces on a second side of the lens blank which, using the current method, compounds the errors and inaccuracies. After the first side is cut as above, the wax holding the lens blank is dissolved and the blank is transferred and adhered to a second dopt again using wax. The second dopt must have its end surface formed to match the shape of the first optical surface of the lens being made to allow proper support and seating on the second dopt. Thereafter, the second optical surface may be cut with the lathe. This transfer operation often creates misalignment of the optical surfaces and poor optical resolution for the resulting lens since the second dopt surface itself may not be properly prepared, the lens blank may not be centered or secured in exactly parallel position to its position on the first dopt. Consequently, the second optical surface may be formed at an angular position which compounds the inaccurate angular position of the first optical surface. Indeed, the current method results in rejection of more than 20% of the lenses being manufactured. In addition, frequent handling of the lenses during their transfer from dopt to dopt is extremely time consuming and causes scratching on the lens surfaces which adds expense to the process and contributes to the high rejection rates.
Accordingly, the need was apparent for an improved method for manufacturing optical lenses, and especially intraocular lenses, such that the optical surfaces formed on one or both sides thereof were precisely aligned for proper optical resolution in use. A method and apparatus were also desired which would reduce handling of the lenses during manufacture, would save time and expense, and would increase the acceptance rate during lens manufacture.